Sandy GallinManaged MJ, Mariah, DollyHospitalized with Blood Cancer

4/13/2017 1:43 PM PDT

Sandy Gallin -- who repped the likes of Michael Jackson, Mariah Carey, Cher, Richard Pryor, Barbra Streisand, Whoopi Goldberg, Neil Diamond, Donny and Marie, and many, many others -- is fighting for his life at an L.A. hospital after his cancer came back.

We've learned Gallin has been at UCLA Medical Center in ICU after suffering a relapse of multiple myeloma, a type of blood cancer.

As 2 of his close friends told us, "It looks really bad."

Over the last few days, close friends including Calvin Klein, Jeffrey Katzenberg, David Geffen and many others visited Sandy in the hospital.

Sandy became one of the top Hollywood managers and, with best friend David Geffen, helped run a political machine for the Democratic Party, raising millions for various candidates and causes. Gallin, who is gay, was a big force in gay rights legislation.

The 76-year-old segued into real estate decades ago, and made untold millions buying, rehabbing and selling some of the best properties in L.A.